![]() Long-life pavements can be designed through a judicious and balanced choice of binder properties. Benefit/cost ratios vary by 2–3 fold for test sections of equal Superpave design but different rheological type (sol, sol/gel or gel). Current trials, commissioned by the Ontario government in the 2000s, were designed to refine binder specification tests, by accounting for well-documented phase separation and transformation, associated thermoreversible changes in rheology (gel formation), and to investigate high polymer and fiber modification. Air-blown materials were found to perform poorly and polymer modifiers only provided benefits in softer grades. Studies in the 1990s focused on evaluating the new Superpave™ specification, developed in the United States, to address the increasing use of modified binders in preceding decades. ![]() Trials to investigate this phenomenon confirmed the importance of binder consistency, temperature sensitivity, phase homogeneity and durability. ![]() Using stiffer binders increased stress from cold temperature shrinkage, typically manifesting, for the first time, as rather regularly spaced transverse cracks. In the early 1960s, increasing traffic demanded that transportation agencies use progressively harder asphalt binders to prevent premature wheel path rutting.
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